Light Measurement

The first responsibility of any light meter is to simply measure the quantity of light reflected by the subject. Many light meters measure light using Exposure Values or EV numbers. As you saw in Figure 23, EV numbers provide a very simple and intuitive way to measure amounts of light: the lighter the surface measured, the higher the number.

We also learned that because EV numbers and zones both measure amounts of light that double as they increase, you can use one to represent the other. If one surface reads EV #7 and another EV #8, you could either say that they are one EV number apart or one zone apart.

Note: Because of the conceptual simplicity of this method, many of the examples that follow will use EV numbers to illustrate various principles being explained.

In Figure 27, the meter is telling us that the wall being read is reflecting 15 units of light. Remember that unless these are EV numbers they are arbitrary. On another meter, the same amount of light might be number 11.




FIGURE 27 Meter reading.

When in-camera light meters are in their manual mode they measure quantities of light through some sort of "nulling" system. For example, bright light may cause a needle or a red dot to move up and you may need to turn an aperture or shutter speed dial until you see that the dot is in the center of a scale, or perhaps a needle is lined up with a ring.

Whichever system the meter uses, all it is doing is indicating that either more or less light is reflected by whatever is in the meter's field of view.

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